Dermatoglyphic method of medical genetics

Introduction to dermatoglyphi
All too often when we teach genetics we limit ourselves to the “tried and true “ single gene traits and “shy away” from more complex forms of genetic inheritance. After, all it is difficult enough to explain Mendelian Laws without the added complexity of quantitative variations. Ironically, understanding the relationship between genetic information and phenotypic expression at the organism level has more to do with the interaction of many genes than it does to any one gene in isolation. Dermal ridges are an example of a trait that shows quantitative variation, is inherited, and is easily analysed in the teaching laboratory. Further,sophisticated mathematical treatments need not be applied to teach the relationship between polygenic inheritance and expression.

Dermatoglyphi and development
Dermal ridges originates from fetal volar pads composed of mesenchymal tissue starting at the sixth to seventh week of development. In general, small pads produce arches and larger pads produce loops or whorls. Lateral displacement of the volar pad creates asymmetry of the pattern. Ridges become visible at about 3 months and are completed by the sixth month of prenatal development.

Fingerprinting
A fingerprint is an individual characteristic-
-no two have yet been found to possess identical ridge characteristics.
Fingerprints will remain unchanged during an individual’s lifetime.

Anatomy of the Fingerprint
Skin is composed of layers of cells.
Epidermis (outer portion) and dermis as inner skin.
In a cross section- a boundary of cells separating the epidermis from the dermis is made up of dermal papillae-these determine the form and pattern of ridges on the surface.
Dermal papillae develop in the foetus and remain unchanged during life.

Types of fingerprints

Sir William Hershel-1856
He was the first to use fingerprints.
An English Chief Magistrate in India who used fingerprints for native contracts.

Sir Francis Galton-1888
Sir Francis Galton, a British anthropologist and a cousin of Charles Darwin, began his observations of fingerprints as a means of identification in the 1880’s.
In 1892, he published his book, “Fingerprints”, establishing the individuality and permanence of fingerprints. The book included the first classification system for fingerprints.

Delta
The ridge point nearest the type-line divergence is the DELTA.
-Triangular in shape.
-ALL LOOPS HAVE ONE DELTA.

Core
Core=center of the pattern

Whorls
Whorls-4 distinct groups:
— Plain
— Central pocket
— Double loop
— Accidental
All whorl patterns have type lines and a minimum of two deltas.
Plain and central pocket loop whirl have at least one ridge that makes a complete circuit.
Ridge may be spiral, oval or any variant of a circle.

Arches
Arches least common has 2 patterns- plain arches and tented.
Do not have:
—type lines
— deltas
— or cores

Methods of detecting fingerprints
The method of choice will depend on the surface being lifted or tested.
Hard and non-absorbent surfaces (glass, mirror, tile, etc) require different approaches than soft and porous-paper, cloth, or cardboard.
The most challenging thing an examiner faces is finding the location of latent prints.

Ultraviolet imaging systems
35mm black and white film.
Scene scope excels at detecting prints on surfaces that a forensic light source would find difficult or impossible.

Ninhydrin
The most cost effective chemical development method is Ninhydrin.
Ninhydrin is used on paper, cardboard, or other porous surfaces.
The problem with spraying Ninhydrin solutions is that, since Ninhydrin reacts with amino acids, any exposure to your body, especially to your eyes or lungs, could have serious results. This potentially dangerous exposure is minimised by dipping or painting.

Preservation of developed prints
Once visualised, it must be permanently preserved for future comparisons and possible use in court as evidence.
Camera with close up lens.
Fixed focus to take photographs on 1:1 scale when lens is held exactly flush against the print surface to avoid distortion.
Photograph prints relative location with other evidential items.

Permanent record of prints
If on small surface-transport without destroying the print.
Protect with cellophane bag.
If large surface objects that have been developed with a powder can best be preserved by lifting.
Done with broad adhesive tape.
Fingerprint covered with adhesive side and pulled up, the powder will be transferred to the tape.
Digital imaging may be used to enhance contrast, enlarge details and compare individual points on prints to others in question.